Drive units for windshield wipers are, typically powered by electric motors. In such systems a wiper arm including a wiper blade is attachable unrotatably on the drive shaft of the drive unit which is drivable in pendulum motion and the direction of rotation of which is reversible. A drive unit of this type can also have an electric motor rotating in the same direction of rotation. A gear unit is coupled directly to the electric motor, and the drive shaft of the gear unit is drivable in pendulum motion and can be equipped with a wiper arm in an unrotatable fashion, as described hereinabove. In addition, a drive unit for windshield wipers can include a supporting structure on which a motor-and-drive unit and one or more wiper shafts drivable in pendulum motion are mounted.
In general, drive units for windshield wipers of this type are fitted to the vehicle body by way of vibration damping elastomeric fastening elements, which are undetachably fixed on predetermined attachment points of the drive unit. To this end, assembly screws extend through the vibration damping elements.
To simplify the assembly of the drive unit to the vehicle, it is known to retain the assembly screws in the assembly position on the drive unit for windshield wipers so as to be rotatable about their axes but undetachable. Thus, the drive unit for windshield wipers is supplied as a complete unit with the fastening screws preassembled thereon for mounting to the vehicle. Advantageously, there is no need for additionally manipulating the assembly screws when fitting the drive unit for windshield wipers to the vehicle.
The publication DE 40 36 367 A1 discloses a drive unit for windshield wipers wherein the assembly screws are retained in their assembly position by a detachment prevention means. The assembly screw extends at each individual attachment point through an elastomeric vibration damping element fixed to the windshield. Before this action, a respective spacer sleeve is inserted into the through-bore of the elastomeric vibration damping element. As a detachment prevention means, a disc which is resiliently elastic to a certain extent and includes a hole is slipped onto the part of the threaded stem of the assembly screw which projects from the vibration damping element. The hole in the disc is smaller than the thread diameter of the assembly screw so that the edge of the hole or portions thereof are clamped on the threaded stem of the assembly screw in a resiliently elastic manner and retain the assembly screw in the desired position. The disc of the detachment prevention means can be made of a thin spring steel sheet or any hard plastic, such as hard polyvinyl chloride (PVC).
A disadvantage of the described assembly screw detachment means is that a disc made of hard plastic may be broken during warehousing or transport or assembly. Thus, reliable detachment prevention is not ensured in any case.
Further, prefabrication of the drive unit for windshield wipers requires excessive assembly work because the discs for providing the detachment prevention of the assembly screws must be manipulated separately.
An object of the present invention is to provide a reliable detachment prevention means for assembly screws on a vibration damping attachment of a drive unit for windshield wipers with minimal effort during assembly.
This object is achieved according to the present invention by a vibration damping attachment of a drive unit for windshield wipers of automotive vehicles wherein the opening of the vibration damping element is closed by an elastomeric diaphragm attached to the vibration damping element for providing the detachment prevention. The diaphragm has a central hole with a smaller inside diameter than the thread diameter of the assembly screw. When the assembly screw is inserted into the opening of the vibration damping element, the central hole in the diaphragm is expanded by the threaded stem, whereby the edge of the central hole is clamped with the threaded screw stem. Thus, the assembly screw is held captive in its assembly position on the vibration damping element.
The elastomeric diaphragm fastened to the vibration damping element will not be ruptured. Thus, a reliable detachment prevention means for the assembly screw is provided. The need for an additional part providing the detachment prevention is obviated by attaching the elastomeric diaphragm to the vibration damping element which, in turn, is fixed to the drive unit for windshield wipers. Undetachable preassembly of the assembly screws in their assembly position on the drive unit for windshield wipers necessitates considerably less mounting efforts compared to the state of the art described.
One favorable aspect of the detachment prevention feature is that irrespective of the prevailing geometric shape of the elastomeric vibration damping element, it is possible to cement or vulcanize a diaphragm of equal elastomeric material to the frontal end of the vibration damping element. The central hole in the elastomeric diaphragm may be made either before or after attachment of the diaphragm to the vibration damping element.
A preferred embodiment of the vibration damping element includes designing the elastomeric diaphragm integrally with the vibration damping element. This is particularly favorable for low-cost manufacture of the vibration damping element with detachment prevention for the assembly screw according to the present invention.
It is thereby rendered possible to manufacture a required vibration damping element with integrated assembly screw detachment prevention in one single working step, for example, by injection molding.
In another preferred embodiment, the vibration damping element with assembly screw detachment prevention has an which elastomeric diaphragm forms a bottom for the opening of the vibration damping element in which the assembly screw is inserted.
It is necessary for the reliability of the assembly screw detachment prevention that the assembly screw is retained by the diaphragm with a sufficiently great amount of elastic clamping force. The thickness of the elastomeric diaphragm must be varied accordingly. Small drive units for windshield wipers mostly require relatively low fastening forces on the vehicle. In this case, relatively small assembly screws are sufficient. To ensure reliable detachment prevention for such small assembly screws, it is sufficient that the thickness of the diaphragm is approximately 0.5 times the pitch of the assembly screw. In comparison thereto, correspondingly great fastening forces and, thus, correspondingly large assembly screws are necessary for large-size complex drive units for windshield wipers as used, for example, on motor trucks or buses.
In order that such large assembly screws are reliably retained on the drive unit, a correspondingly large amount of elastic clamping forces of the diaphragm is necessary. It is advisable in such a case that the thickness of the diaphragm is approximately 1.5 times the pitch of the assembly screw. A design of the vibration damping attachment wherein the elastomeric diaphragm has a slotted oval shape is expedient in cases where slight lateral shifts are necessary to accurately position the drive unit during the assembly of the drive unit for windshield wipers on the vehicle. The slotted oval shape of the hole in the diaphragm permits sliding motion of the assembly screw with respect to the hole by a certain amount within its longitudinal extension. In this respect, it is advisable to design the hole of the diaphragm in dependence on the prevailing conditions.
Apart from vibration damping elements which, in the line of vision, in an axial direction of the opening of the vibration damping element, have a circular shape and the opening of which for the assembly screw, accordingly, has a circular cross section, in practice, vibration damping elements have also been applied which have an oval shape and, accordingly, an oval opening for the assembly screws. Such shapes are applicable also to vibration damping elements having an assembly screw detachment prevention according to the present invention.
When the vibration damping element and its opening have an oval shape, it is advantageous that the diaphragm has a slotted oval hole which extends in the longitudinal direction of the vibration damping element. Such a design is particularly favorable if the drive unit for windshield wipers must be displaceable by a slight degree for precise adjustment during fitting to the vehicle. The vibration damping elements must then be aligned with respect to their oval shape alongside the necessary direction of displacement.
A particularly simple and inexpensive design of a vibration damping attachment is possible when acute assembly screws are used. Preferably, the hole in the diaphragm is produced by the tip of the assembly screw in this case, when the assembly screw is inserted into the opening of the vibration damping element for preassembly purposes. Thus, the separate provision of a hole in the diaphragm is not necessary.
In cases where a spacer sleeve, known per se, with a collar on one side is inserted into the opening of the vibration damping element, it is advisable that in the position of the spacer sleeve where the collar of the spacer sleeve abuts on the frontal end of the vibration damping element, there is at least a small distance between the end of the spacer sleeve disposed in the opening and the elastomeric diaphragm.
This provision is intended to prevent that the frontal end of the spacer sleeve inserted into the opening will squeeze or even punch out the diaphragm during the assembly or later when the drive unit for windshield wipers is mounted on the vehicle. In this case, reliable assembly screw detachment prevention would not be ensured or would even be impossible when the drive unit for windshield wipers is dismounted from the vehicle.